JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://mindvelopers.com/jquery.countdown.min.js"></script>
<div id="clock"></div>

JavaScript

Date.prototype.yyyymmdd = function() {
   var yyyy = this.getFullYear().toString();
   var mm   = (this.getMonth() +1).toString();
   var dd   = this.getDate().toString();
   return yyyy + (mm[1]?mm:"0" + mm[0]) + (dd[1]?dd:"0" + dd[0]);
};

var data1 = new Date();
var data2 = new Date (data1);

var addDays = 1;
var addHoras = 21;

data2.setDate(data1.getDate() + 1); // Adiciona +1 dia
data2.setHours(data1.getHours() + addHoras); // Adiciona +21 hrs

$('#clock').countdown(data2, function(event) {
    $(this).html(event.strftime('%D dia(s) %H:%M:%S'));
});